Percutaneous Transluminal Angioplasty and Stenting Reconsidered

Originally developed by the Swiss physician Andreas Gruentzig as a less traumatic alternative to CABG, and first performed in the U.S. in 1978, percutaneous transluminal coronary angioplasty (PTCA) has soon emerged as a mainstream revascularization modality, particularly well-suited for singular concentric coronary artery occlusions.

PTCA is a minimally invasive procedure intended to restore normal (or nearly normal) blood circulation in occluded coronary arteries through a radial dilation of atherosclerotic plaque and its compression against arterial wall with transluminally-placed inflatable balloon.

In PTCA procedure, occluding coronary lesion is first crossed with appropriate guidewire, which is typically inserted under fluoroscopic guidance through a puncture in femoral artery and brought to the treatment site via iliac artery and aortic tree. A special balloon-tipped catheter is then deployed over the guidewire across the targeted lesion and repeatedly inflated to provide a required reopening of the arterial lumen. The catheter is then withdrawn and arterial puncture is secured with the use of external pressure aids or special vascular puncture closure device.

Despite some indisputable benefits of “plain old balloon angioplasty,” its ultimate clinical efficacy was seriously compromised by the disappointingly high rate of restenosis that ran as high as 50% at six months and typically required re-intervention. Introduction of coronary bare metal stents (BMS) in the early 1990s allowed to partially alleviate that problem by reducing the average restenosis rate by about one-half. Stents also helped to virtually eliminate many of the complications of conventional angioplasty, such as abrupt and unpredictable collapse and closure of the vessel, which resulted in emergency bypass surgery.

Since the introduction of bare metal coronary stents, the usage of angioplasty expanded considerably, supplanting CABG as the most commonly employed modality of myocardial revascularization.

By the beginning of the past decade, though, growth in PTCA and coronary stenting caseloads started to slow down in the U.S., Europe, and Japan reflecting significant penetration of technically feasible CAD indications and a disappointingly high rate of post-PTCA and in-stent restenosis. The problem of restenosis represented a single major handicap of coronary angioplasty/stenting, which hampered its ultimate clinical outcomes and often forced a revision and eventual conversion to bypass surgery.

In the opinion of many leading clinicians and industry’s analysts, introduction of drug-eluting stents (DES) represented the single most important innovation in endovascular therapy, since the advent of stenting and angioplasty that was bound to have a revolutionary impact on interventional cardiology practices. In addition to effectively remedying the nagging problem of coronary restenosis (by reducing its rates to mid-low digit figures), the drug-eluting devices also enabled interventional cardiologists to successfully manage coronary indications and patient caseloads that were traditionally deemed unsuited for angioplasty and stenting. The latter include treatment of small diameter vessels, long and bifurcated lesions, left main artery and multivessel disease, as well as expanded coverage of high-risk patient cohorts with advanced diabetes, renal insufficiency/failure and recent major AMI.

Unfortunately, in the middle of the past decade, one could witness a gradually growing concerns about relatively high incidence (compared to BMS) of late and very late stent thrombosis (often leading to AMI and death) and overall safety of DES, that have prompted several warning letters, but were generally ignored due to initial exuberance about superb antirestenotic performance of DES technology. Following a release of disturbing findings from several major studies in 2006, the cited concerns appeared to reach a “critical mass” bringing the safety issues to the forefront of renewed DES debates and ultimately prompting a very significant decline in DES usage and cumulative PCI procedure volumes in the U.S. and Europe.

In the view of many leading clinicians, the higher propensity of drug-eluting stents to late (and very late) thrombosis is stemming from the very nature of current DES technology which is focused primarily on prophylaxis of binary restenosis via distortion and inhibition of natural healing processes involving neointimal outgrowth. The latter, by definition, lead to a significantly delayed epithelialization and protracted stent struts exposure to the blood stream, which have been identified as the main sources of thrombogenicity. According to multiple IVUS and pathology studies, incomplete endothelialization of DES (with associated bare strut exposure and device malapposition) is commonly observed at 3 to 4 years post-implantation, in contrast to full epithelial coverage of BMS occurring at 5 to 6 months after stent placement.

Early termination of dual (aspirin-clopidogrel) antiplatelet regimens due to patient’s non-compliance, serious complications, or other reasons appears to represent another major contributing factor to onset of late thrombotic events. Based on available data, the vast majority of DES-related thrombosis episodes tend to occur at 1.0 to 3.5 years post-implantation, or after the recommended 12-month period of dual antiplatelet therapy. According to clinical literature, other factors implicated in the occurrence of late and very late DES thrombosis include presence of inflammatory polymer on stent, incomplete drug elution, rate of drug elution, cytotoxicity of chosen drug, as well as poor DES patient selection (e.g., utilization of DES in high-risk diabetics, and their off-label uses in small diameter vessels, patients with long and bifurcated lesions, etc.).

Most of the cited problems were effectively addressed by the next-generation DES devices that combine sophisticated cobalt and platinum alloy stenting platforms and biodegradable drug coatings with super-low-profile delivery and minimally traumatic deployment systems.

It is assumed that clinical efficacy and utility of DES technology would be significantly enhanced with the advent of specialty bifurcation-targeting devices, vascular healing-focused biopharmaceutical coatings, and in increased adoption of fully biodegradable stenting systems.

For forecasts of off-pump CABG, on-pump CABG, primary PCI with stenting, and drug-eluting stent-based PCI procedures (separately for U.S. Western Europe, Asia/Pacific and Rest of World), as well as all major cardiovascular surgical and interventional procedures, see Report #C500, “Global Dynamics of Surgical and Interventional Cardiovascular Procedures, 2015-2022.”